21 Luxeon Z LED's circuit options

[ElectroLumen]

Hello,

Brand new here and I hope this is the best place for this post. I am working on a fixture using Luxeon Z leds (http://www.luxeonstar.com/assets/downloads/DS120.pdf) of which a 3 tier fixture ( it is going to be modular) uses 21 LED's. At this point I am exploring the wiring restrictions and options. When testing the LED's running them at their suggested current of 700ma and 500ma I found that they were way over the brightness I am looking for. I think that even running these at 350mA would be sufficient for lumen output per LED. I will be using a constant current driver for these but am really looking to see what would be a safe and efficient way to run this many of these LEDS. That said there is limited room for wiring and I would also need to work within UL Low voltage standards (ideally).

When looking at wiring in parallel even under driving these the total current needed would be 7.35A, which seems like it may not be a great idea, the wires would also need to account for current.

I want to avoid using resistors since the space is limited and the wasted energy involved. That said I have very limited experience with LED driving in this type of design and could be misplacing my approach. I have attached an image of a combination circuit that seems to make sense and the specs of the LEDs for reference. Please take a look and let me know if you have any thoughts or ideas on creating such a fixture. FYI the lumen output does not need to be 100% and I actually think these should be run at 1/3-1/2 the maximum brightness since its mostly decorative.

> Combination circuit and led specs > https://i.imgsafe.org/fbb3f3e9f2.jpg

If I have not provided any info needed please let me know, I appreciate any help I can get on this project.

Thanks.

 

[evilc66]

So, you can't run unequal strings in parallel. The total forward voltage of each string has to match or else there will be a current imbalance (the lowest voltage string will draw the most current). Best way to approach this would be with a driver per series string. Meanwell's LDD series LED driver would be a good fit here, and you can run everything on a 48v power supply with decent efficiency (48v will keep you in low voltage territory)

 

[ElectroLumen]

Hey,

thanks for the response, I have looked at the Meanwell LDD series. Just to be clear, the suggestion is to use 1 LDD-H driver per string on the fixture? So with three tiers I would use 3 of these drivers and a http://www.rapidled.com/ldd-h-4s-driver-board/ to connect the drivers to a DC power source?

Thanks again,

J

 

[ElectroLumen]

Thanks again for the information. To Clarify I wanted to be sure I understand, you are suggesting using a mean well LDD to power each string so that all strings receives the same current? So 3 Ldd's for 3 strings? I was also curious if I tried to run these in parallel would there be any big issues and do you know of any drivers that could do this. Like I said originally the LEds are very bright and I think running them at 350mA still provide enough light.

Thanks,

J

 

[evilc66]

Yes, one LDD per string. The reason is that you can't run strings of different length in parallel. Seeing as each string is a different length, a separate driver is required. There is no problem connecting the input power to the LDDs in parallel to the power supply. Just make sure that whatever power supply you use has enough current. The board from RapidLED will work very nicely for what you are planning.

The LDDs are dimmable, and the RapidLED board has inputs for a pwm signal (can't just use potentiometers here) if you care to use that feature. If you don't, the jumpers at the top of the board will need to be removed so that driver output turns on. That jumper is there to connect a pull down resistor to the dimming pin on the driver for when you use a dimming signal with the board.